Matrix print wire solenoid

Abstract

A matrix print wire solenoid has a small diameter print wire which wire is propelled against printing paper and inking ribbon by the linear motion of the solenoid plunger, to which the print wire is attached, in an improved impact printer having a plurality of solenoids positioned in a row for use in dot matrix printing. The solenoid features a low cost construction, a reduction in size, and increased operating speed, and has pole pieces which are separated by an inner gap and which pieces are aligned with a coil bobbin which provides a guide surface for the armature plunger. The space between the plunger and a forward bushing or spacer is occupied by a coil spring which has one end seated over a portion of the armature and the other end seated against the face of the bushing. The coil bobbin defines an air gap between one pole piece and the armature.

What is claimed is: 
     
       1. A solenoid for moving a print wire, comprising a housing, a   first pole piece enclosing one end of said housing and having an aperture therethrough, a   second pole piece enclosing the other end of said housing and having an aperture therethrough, an   armature positioned in the aperture of said second pole piece, said print wire being secured to said armature and movable therewith upon movement of said armature, a   coil for providing magnetic flux in a path through said housing and said pole pieces to cause axial movement of said armature and said print wire, a   sleeve encircling a portion of said armature and a portion of said first pole piece for containing said coil, said sleeve having an enlarged diametral portion engaged by said first pole piece for positioning said first pole piece in axial relation with said armature and providing a gap therebetween, and   means connecting said first pole piece and said armature for maintaining said armature in fixed position prior to energization of said coil, for permitting said armature to move along said gap upon energization of said coil, and for returning said armature to said fixed position upon deenergization of said coil.   
     
     
       2. The solenoid of claim 1 wherein said connecting means comprises a coil spring operating in the aperture of said first pole piece and through which said print wire passes. 
     
     
       3. The solenoid of claim 2 wherein said first pole piece includes an enlarged aperture therein and there is provided a bushing member seated in said enlarged aperture and engaged by said coil spring at a fixed plane of said first pole piece. 
     
     
       4. The solenoid of claim 1 wherein said second pole piece includes an annular recess therein for engagement by one end of said sleeve to fix the axial position thereof in relation with said second pole piece. 
     
     
       5. The solenoid of claim 4 wherein said sleeve includes an elongated annular recess at the other end thereof for seating engagement by said first pole piece and said sleeve one end is seated in said annular recess of said second pole piece. 
     
     
       6. The solenoid of claim 1 wherein said armature comprises an inner portion of non-magnetic material and an outer portion of magnetic material. 
     
     
       7. The solenoid of claim 6 wherein said first pole piece and the outer portion of said armature each define a sloping end surface forming said gap therebetween. 
     
     
       8. In a printer having at least one solenoid for driving a print wire for printing characters, said solenoid comprising a coil energizable in response to magnetizing current, an   apertured first pole piece adjacent one portion of said coil, an   apertured second pole piece adjacent another portion of said coil, an   armature positioned between said pole pieces and axially slidable a precise distance to drive said print wire, a   bobbin member disposed to engage said pole pieces and containing said coil in a form to provide magnetic flux in a path through said pole pieces and said armature, said bobbin having an enlarged inside diameter portion for engagement by said first pole piece to fix the position thereof in relation to the armature, said second pole piece having an enlarged inside diameter portion for engagement by said bobbin member to fix the distance of said second pole piece from said first pole piece, and   means operably associated with said first pole piece and with said armature for maintaining said armature in one position prior to energizing said coil, for permitting said armature to axially move along said bobbin member upon energizing said coil, and for returning said armature to said position after deenergizing said coil.   
     
     
       9. In the printer of claim 8 wherein said operably associated means comprises a coil spring operating in the aperture of said first pole piece and through which said print wire passes. 
     
     
       10. In the printer of claim 9 wherein said first pole piece includes an enlarged aperture therein and there is provided a bushing member seated in said enlarged aperture and engaged by said coil spring at a fixed plane of said first pole piece. 
     
     
       11. In the printer of claim 8 wherein said second pole piece includes an annular recess therein to form a shoulder for engagement by one end of said bobbin member to fix the axial position thereof in relation with said second pole piece. 
     
     
       12. In the printer of claim 11 wherein said bobbin member includes an elongated annular recess at the other end thereof to provide a shoulder for seating engagement by said first pole piece and said bobbin member one end is piloted in said annular recess of said second pole piece. 
     
     
       13. In the printer of claim 10 wherein said coil spring is seated in said bushing member and said armature includes an end portion encircled by said coil spring. 
     
     
       14. In the printer of claim 8 wherein said armature comprises a core portion of non-magnetic material and a shell portion of magnetic material surrounding said core portion. 
     
     
       15. In the printer of claim 14 wherein said first pole piece and the shell portion of said armature each define a conical-shaped end surface spaced from each other and forming a gap therebetween.